1. Field of the Invention
This invention relates to an apparatus and method for automatically monitoring machining processes and particularly, for monitoring a machining processes, as a function of the machine's mechanical vibration and power consumption.
2.Description of Related Art
Tool wear, loss of coolant, broken tools, and excessive vibrations are problems of machining apparatus and processes that use tools to grind, cut, drill, or in some way mechanically remove metal or other material during the machining process. These problems can cause reduced or unacceptable levels of quality, excessive scrap rates and increased production costs. During the grinding process dull tools, such as grinding wheels, or loss of machine coolant may easily go undetected by the machine operator and lead to sometimes expensive machinings having to be reground or scrapped altogether. The use of automated machining devices including robots, machining cells, and other unattended machines requires some means of machining process monitoring whether it be manual or automated. Several automated tool monitoring devices have been developed to monitor tool wear. These tool monitors produce signals that warn human operators to take corrective action or send signals to computerized machine controllers which then initiate automated corrective procedures.
Prior tool monitoring devices use complicated and expensive probes that may require modification of the grinding machines or machining process. One such device is described in U.S. Pat. No. 4,295,301 entitled "Dressing Apparatus with Means for Detecting Grinding Wheel Wear", by Barth et al. and has a complex movable intrusive probe which must contact the grinding wheel and a probe movement detection device as well as an accelerometer.
Acoustic energy sensor based tool monitoring systems have also been found to require frequent calibrations as well as requiring more complicated less accurate apparatus than that of the present invention.
Other tool wear or condition monitors are known and used in the industry such as the ATAM system by IRD Mechanalysis which uses an accelerometer to produce a signal indicating vibrational patterns of machines which change as the cutting tool wears which requires a great deal of calibration each time a new tool is used.
The WIBRA tool condition monitoring system produced by the WIBRA Company of Sweden, as described in their brochures which are incorporated herein by reference, uses only accelerometer data and requires that the system be recalibrated each time a new tool is used. It also is most accurate when the tool is damaged unlike the present invention which seeks to prevent production of a machining with less than minimum quality levels.